The invention relates to a circuit arrangement for optionally (i.e. selectively) amplifying one of at least two signals.
Circuit arrangements of this type can, for example, be used in video signal processing circuits in which video signals from different video signal sources are processed for conveyance to a video signal sink. Generally however, their use in the processing of any type of signals is alternatively possible.
With such a junction of signal paths from different signal sources to a signal sink, it may be recommendable to interrupt in a predetermined operating state signal sources to which at that instant no signals are applied from the associated signal sources. In the inhibited state, the voltage difference between the signals from the signal source of the interrupted signal path and the signal voltage of the operative signal source is superimposed on such signal path interruptions which are of the switchable type. These voltage differences are composed from the amplitudes of any signal voltages assigned to the signals as well as potential differences in the signal path and can assume considerable values. The switchable signal path interruptions must then be structured such that they are capable of withstanding these voltages.
Preferably, circuit arrangements of the defined type are provided in integrated circuits on semiconductor bodies which as regards their geometry and their manufacturing process must first of all be designed such that they enable a signal processing which has the shortest possible delay and the lowest possible power. The individual circuit elements of integrated circuits of this type can often be loaded with only a very low electric voltage. If a switched-mode signal interruption is implemented in this technique, there is a risk of voltage breakdowns and consequently the destruction of the integrated circuit.